The development of paint for use in places where the bacteriostatic activity is essential represents a challenge for this industry, particularly in hospital environments where the goal is that all painted surface will prevent the formation of bacteria colonies. These coatings should show high bactericidal power, low or even no toxicity for human beings and low environmental impact; their cost should be reasonable and within the range of other industrial paints.
Several strategies have been followed to reach to these objectives. For instance, modified bacteriostatic agents have been developed to be included in the polymer network. This approach to the problem has several drawbacks. On the one hand, it is difficult to formulate broad spectrum antibacterial agents compatible with an industrial process such as the manufacture of paint. Besides, these agents tend to degrade quickly severely limiting the product life time. Another strategy has been the use of metal salts such as silver, encapsulated in natural clay such as zeolites EP 0 116 865 (1984). In this case, the clay must be processed to make it compatible with the paint components. On the other hand, in these cases the bactericide must migrate or diffuse from the interior of its capsule up to the place where it should exert its bactericidal activity.
In the last few years, the use of TiO2 photocatalytic nanoparticles (NP) for the broad spectrum antibiosis has been successfully experimented. (Wang, R., Kashimoto K., Fujishima A., et al; Nature 388 (1997) 431, Hagfeldt A., Gratzel M.; Chem. Rev. 95 (1995) 49, Williams A. J., Pin C. M.; Environ. Sci. Tech. 32 (1998) 2650) and patent publication WO2006/061367. Combined NP systems of TiO2/M+ (M=Cu, Au, Ag) have been used as particles with bacteriostatic properties in plastics, glass coatings, fibers and material for medical purposes (Oloffs A. et al; Biomaterials 15 (1994) 753; Kawashita M., Tsuneyama S. et al; Biomaterials 21 (2000) 393; Q. Cheng, Ch. Li et al; Appl. Surf. Sci. (2005) and Patent EP0251783 B1). In these compound systems, the monovalent metal plays a key role when reacting with certain essential amino acids of the bacteria. However, in a paint, the presence of pigment (TiO2) with photocatalytic properties is counterproductive, since it may degrade the polymeric film.
Also, one of the components of paint are inorganic powders, called fillers which are used to modify the paint properties such as abrasion resistance, outdoor resistance, permeability, gloss, etc. Since inorganic fillers represent a high percentage in volume of a dry paint film, their use as carrier of bactericidal components would result in a suitable method for providing the bactericidal properties to the whole volume of a coating formulation such as a paint.